1. Technical Field
The present invention relates to a cylindrical shaft, a transport roller, a transport unit, and a printing apparatus.
2. Related Art
In the past, various printers have been provided as printing apparatuses. These printers are configured such that recording media such as paper are transported to a printing unit by a transport roller (paper feeding roller) and a driven roller, and after printing is performed, the media are discharged by the discharge roller (driving roller) and the driven roller (GIZA roller).
In such a printer, the transport roller rotates in a state where the paper is interposed between the transport roller and the driven roller, so that the paper is moved in a sub scanning direction perpendicular to a moving direction of a carriage. Since the paper must be transported to the recording position with high accuracy and be sequentially fed in synchronization with the printing speed, a high transportation force is required.
In order that the transport roller has a high frictional force, Japanese Patent No. 3271048 discloses a technique in that a large number of protrusions are formed on a circumferential surface of a metallic round bar by an embossing work.
In the technique, there is a problem that workability is very poor at forming the protrusions on the shaft-like (cylindrical) surface along the circumferential direction. In addition, since a solid material is used, the cost is also increased.
In view of the above situation, JP-A-2006-289496 discloses with the aim of cost reduction, in that a metal plate is subjected to a bending work to form a shaft (cylindrical shaft) in a cylindrical shape (hollow shape) and the cylindrical shaft is used instead of the solid metallic round bar member. That is, in JP-A-2006-289496, there is proposed a cylindrical shaft which is formed of a metal plate by bonding a pair of ends facing each other, and each of the ends is provided with a convex portion which protrudes from the end and has a width becoming wider as a position moves away from the end, and a concave portion which is dented from the end and has a width becoming wider as a position moves away from the end. In addition, the convex portion and the concave portion of one end are fitted to the concave portion and the convex portion of the other end.
However, when the cylindrical shaft as disclosed in JP-A-2006-289496 is used as the transport roller in order to achieve cost reduction and weight reduction, it is difficult to make the cylindrical shaft have a high frictional force.
For example, it may be considered that the surface is beaten by a pressing work to form protrusions as in the case disclosed in Japanese Patent No. 3271048. However, in this case, since the shaft is hollow, it is easily deformed.
In addition, in the cylindrical shaft disclosed in JP-A-2006-289496, the convex portions and the concave portions are formed on a pair of the ends facing each other over the entire region (entire length) in the length direction, and the convex portions and the concave portions of the pair of the ends are fitted to each other. That is, in the joining portion between the pair of the ends, fitting sections between the convex portions and the concave portions are continuously formed over the entire region (entire length) in the length direction.
When the fitting sections between the convex and concave portions are formed over the entire length of the joining portion as described above, it is difficult to fit the convex and concave portions in the fitting sections as it was designed, and to fit the convex and concave portions to each other. As a result, deformation or distortion easily occurs on the entire of the cylindrical shaft. In addition, roundness or deflection with a set value or more is hardly obtained, so that it is difficult to obtain the shape and the dimension with good accuracy.
Therefore, when the cylindrical shaft which is insufficient in the accuracy of the shaft and the dimension is applied to the transport roller as described above, it may act as one factor causing uneven transportation. In addition, a so-called ink jet printer, which forms images by ejecting fine droplets, necessitates very high accuracy in feeding paper. Therefore, in particular, the occurrence of uneven transportation caused by the groove becomes problematic.